How to replace the emulsion tubes on a Mk1

[maelstrom]

Hello everyone,

I am Blair and our business is LiteTek. I am not trying to sell anything to you.

Sorry I don't have a TRX just a 4 cylinder. Anyway one of my customers mentioned the forum and I know that the needle/emulsion tube wear for Mikuni BDST's is worse for big twins.

Anyway I thought to give some of my take on this.

First of all the wear occurs at idle where the needle is closest to the emulsion tube and the pulses are ratting the poor things to death. So there are two parts to improving this.

 

Part 1 - The Needle:

Reduce the tendency for the needle to vibrate as much as it does. On the 4 cylinder 250cc Yamaha the same problem was addressed in the very last models by sealing the top of the needle. As shown in the first pic.



 

Honda do something similar with the downdraft carbs on their 250cc four.



 

This sits over the top of the needle and totally seals it.

 

Now trying to do something like this with standard BDST will prove to be difficult. My idea was to machine an o-ring groove into the needle bore in the slide. Fit an o-ring and the needle passes through that. Just haven't got around to doing it and to make matters worse I just got a set of FCR's.

 

Part 2 - The Emulsion Tube

So these being made of brass is not good from a tribological point of view. So what I chose to do was to sleeve some used emulsion tubes with a polymer. 



These are machine reamed and checked with pin gauges. Now the customer that I did these for has not used them, so much for our field trials. If one of you guys would like to try a set out then give me the number of your worn emulsion tubes and I will see what bits I need to get. If it is doable then I could do them for you and you could try them out.

 

Some of you may have seen my guide for BDST's here. https://litetek.co/Guide_MikuniBDST_Rebuild.html  and this is the Keihin version I did which has some extra hints that I have not put into the Mikuni one yet. https://litetek.co/Guide_Keihin_Rebuild.html

Cheers

Blair